First, in one solution if you remove the last digit of the longer number, it will be the same as the shorter one. In this case the shorter one is (n div 11).

Now if you force the last digits of both numbers are the same, it can only be (n div 2 mod 10) or (n div 2 mod 10+5). Store this as a suffix, cut the last digit off n, and do all above for the new but smaller n.

I don't know if I have explained it clearly. If you still have questions, please mail maigoakisame@yahoo.com.cn